Dual pump control systems

ABSTRACT

Disclosed is a system for regulating and controlling at least two compounded pumps in a well drilling operation where one pump is regulated in a fixed relationship relative to the regulation of the other pump. The functional control of the two pumps can be interchanged between a manual control location and a remote control location. Either pump can be selected as the prime control unit. The functional control parameter for the manual and remote controls may be compared to one another and regulated relative to one another to maintain a parity therebetween so that &#39;&#39;&#39;&#39;bumpless&#39;&#39;&#39;&#39; transfer of the functional controls from one location to another can be obtained.

' United States Patent 11 1 Dower 1 Nov. 4, 1975 [73] Assignee: Drill-Au-Mation, Inc., Houston,

Tex.

[22] Filed: Oct. 4, 1973 [21] Appl. No.: 403,344

{56] References Cited UNITED STATES PATENTS 5/1931 Warren 417/5 4/1933 Soderberg 417/5 5/1933 Allen 417/4 1/1959 Osterhout et al. 417/2 6/1961 Accaro 417/33 3,039,543 6/1962 Loocke 175/38 3,251,534 5/1966 Strecker.... 417/6 3,362,487 l/l968 Lindsey 175/38 Primary Examiner-William L. Freeh ABSTRACT Disclosed is a system for regulating and controlling at least two compounded pumps in a well drilling operation where one pump is regulated in a fixed relationship relative to the regulation of the other pump. The functional control of the two pumps can be interchanged between a manual control location and a remote control location. Either pump can be selected as the prime control unit. The functional control parameter for the manual and remote controls may be compared to one another and regulated relative to one another to maintain a parity therebetween so that bumpless transfer of the functional controls from one location to another can be obtained.

16 Claims, 2 Drawing Figures DUAL PUMP CONTROL SYSTEMS BACKGROUND OF THE INVENTION This invention relates to control systems, and more particularly, to control systems for controlling the relationship between dual pumps in a well drilling operation. Specifically, the speed of one pump is automatically controlled in a predetermined relationship relative to the speed of another pump.

In a typical rotary drilling operation through earth formations, a tubular drilling string carries a drilling bit at its lower end and by rotation of the string and weight on the string, the drilling bit cuts through earth formation strata and forms a well bore. To remove the earth cuttings from the path of the bit and to cool the bit, a system for circulating a fluid (sometimes called mud) into and out of the well bore is used. The mud circulation system starts with a surface located pump means which picks up a drilling fluid or mud from a surface tank and delivers the fluid to the interior of the tubular drilling pipe or string where it travels to the drilling bit and exits therefrom in the form of a jet or other type of fluid course. The fluid then moves upwardly in the annulus between the outer surface of the drill pipe and well bore and carries with it cuttings from the earth formations. The return fluid is delivered or returned from the annulus to the surface tank for recirculation.

The proper sizing or selection of mud pumps with respect to the capacity of the pumps for volume and pressure output required is a major factor in the drilling of a well. This is particularly true where the output of two or more pumps are combined for the purpose of increasing the mud circulation rate and decreasing the cost of drilling. Sometimes, a pump will operate poorly and result in excessively high maintenance costs if the pump output is increased for the purpose of increasing the drilling rate. This can be especially true in instances where the pressure output is substantially increased. Hence, the pumps should be operated with care in regard to both efficiency and cost factors.

Increased maintenance costs and decreased life occur when the capacity of the pump is too small for the operation. On the other hand, using a pump that has excess capacity is expensive in terms of high initial cost and the costs of moving it from location to location. In other words, it is desirable to use a pump or pumps that are adequate for the task and this means using the pump or pumps at a top operating efficiency under the most severe conditions.

Use of two pumps can have advantages. For example, if two pumps are placed in parallel, the volume output is increased. When two pumps are so used and they are effectively protected, the compounding of the pumps has advantages over the use of a single large pump. For example, if one of two pumps is stopped for one reason or another, the drilling operation is not seriously hampered because one pump is still operational. With a single pump, its capacity is affected by its liner size. Thus, the liner is changed throughout the drilling operation as the pump capacity requirements change. Where there are two pumps, they can jointly cover a greater range of capacity and more days of operation can be obtained without changing liners.

A pump has a volumetric output which is a function of the RPM (revolutions per minute) or speed of the prime motor or engine. The volumetric output of a given RPM results in a defined pressure which is determined as a function of the circulatory system. It will therefore be appreciated that the horsepower requirement of the prime mover is dependent upon speed, volumetric output and pressure. The horsepower output of the prime mover is typically regulated by a throttle control which regulates its output. In the use of two or more pumps, their volumetric outputs are combined to obtain optimized output conditions. Where pump outputs from two or more pumps are combined, however, it is desirable to have regulation of the control of the respective pumps for controlling the'total volumetric output requirements under varying conditions.

SUMMARY OF THE INVENTION The present invention concerns itself with a system for dual or simultaneous control of at least two pumps for a well drilling operation. The control system includes means for manual control at a rig site and means for remote control from an offsite location. The manual and remote control means are independent and separate from one another. In the remote control means, the functional control for one pump is made dependent upon the functional control for the other pump in a fixed relationship so that the functional control of a primary pump exercises a slaved. functional control over a secondary pump. The remote control means are adapted to permit an exchange of the primary control function between the pumps and to permit an exchange of control functions between manual and remote control means. The pumps are controlled by pneumatic pressure and selectively operative valve means can couple either the manual pressure control means or remote pressure control means to a pump. The remote pressure control means for the prime system provides electrical control signals from a remote location for operating a current-to-pressure converter at the rig location. The pneumatic pressure from the converter functionally controls one of the pumps and is also supplied to a ratio device which reduces or amplifies the input pneumatic pressure by a fixed ratio to supply a functional control pressure for the secondary pump. A pressure comparison system is provided to compare the functional control pressures for the remote control means to the functional control pressure in the manual control means so that the two control means can be regulated or adjusted relative to one another to similar or equal values, thereby permitting a bumpless transfer of the control functions from one location to the other location.

The features and advantages of the foregoing system will be more easily understood from the following detailed description of a preferred embodiment of the system when taken in conjunction with the attached drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of the system embodying the present invention; and

FIG. 2 is a schematic illustration of component details of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, an elemental mud circulation system is illustrated in simplified form for ease of understanding. In FIG. 1 the interior of a tubular casing or pipe string 10 in a well bore (shown in cross-section) is coupled to a well input line 1 l. A mud return annulus 12 is defined between the exterior of pipe string 10 and surface casing for the well bore and is coupled to a mud return line 13. The mud return line 13 from the casing is coupled to shale shakers and other reconditioning devices (not shown) for reconditioning of the mud before it is returned to the mud tank. The various wellknown elements of the reconditioning system are not shown since they form no part of this invention.

To supply the mud to the well bore, the mud in a mud tank (not shown) is drawn into an input conduit 13A for the mud pumps illustrated as 14 and 15. The valves 14A and A, respectively, in the inlets to the mud pumps can be manually operated to cut off the flow to a pump. The pump 14 outputs a flow of liquid to the well input line 11 via a valve 16. The pump 15 outputs a flow of liquid to the well input line 11 via a valve 18.

The mud pumps 14 and 15 (which are conventional) have important functions in the circulation system which include (1) the promotion of the ease of drilling by virtue of developing a liquid flow to provide a jetting action at the bit; (2) the circulation of a sufficient quantity of mud to keep the bit washed clean; and (3) the return of solid earth particles or cuttings to the surface, thereby keeping the hole free of cavings, cuttings and weight material settlings. The density, viscosity and gel strength of the mud used has a bearing on the operation of the pumps in that the pumps are required to maintain a necessary flow velocity to keep the hole clean. I

The mud pumps usually are positive displacement reciprocating types and the horsepower of a pump is a function of the output volumetric flow rate and pressure. At its rated speed, a pump will reach its power rating at the maximum rated pressure for each liner size. To determine the horsepower needed for a given drilling operation, the volume of mud necessary to provide sufficient velocity to remove the cuttings is determined. With the volume of mud determined, the pressure loss and the pressure drops can be determined to find the necessary pump pressure. A pressure-volume relationship can be used then to define the hydraulic horsepower required.

The pump 14 is operated by an engine or motive means 22 while the pump 15 is operated by an engine or motive means 23. The pump 14 and engine 22 or the pump 15 and engine 23, respectively, are functionally combined units so that in the description to follow, the control or operation of a pump or an engine of one unit is synonymous with operation or control of its associated engine or pump. The engines 22 and 23 have clutch means (not shown) for controlling the application of driving power to the pump and throttle means for. controlling the speed of an engine. In FIG. 1, the present invention will be described in connection with a control for the throttles, although it will be appreciated that other regulating means could be controlled. Each of the engine throttles have manually variable throttle controls 24 and 25, which are respectively illustrated for each of the engines for pumps 14 and 15. The throttle controls 24 and 25 are manually operable to adjust a throttle T of an engine by means of a pneumatic pressure control system. In the pneumatic pressure control system between the control 24 and engine 22 is three-way valve 26 which can be independently operated between a position where the pressure control to the throttle T is exercised by the manual control 24 and a position where the pressure to the throttle T is from a remote throttle control 28. Similarly, a threeway valve 27 in the control system couples the manual throttle control 25 to the throttle T of engine 23 in one position and in another position couples the remote throttle control 28 to the throttle T. The remote throttle control 28 provides an alternate, remote control for the engines and is responsive to electrical control signals from a remote location control means 29. When the remote control means 29 is in command of the remote throttle control 28, the pumps are synchronized for operation in fixed relationship to one another in a manner which will be fully described in the discussion to follow.

Referring now to FIG. 2, the components of the remote throttle control 28 and the interrelated control devices for the pumps are illustrated in more detail. For ease of understanding, various pneumatic control valves are illustrated by circles where the semi-circular portion which is shaded indicates a closed or blocked path or condition in a valve and the unshaded semi-circular portion indicates a flow-through or open condition in a valve.

Beginning at the remote control location 29, a potentiometer 30 is schematically illustrative of an electrical control means which is coupled by an electrical path 31 to the remote throttle control 28. In the remote throttle control 28 is a current-to-pressure converter 32. The current-to-pressure converter 32 is a commercially available device, for example, Model 69TA manufactured and sold by the F oxboro Co. The converter 32 is adapted to respond to input electrical current signals and provide a proportionate output pneumatic pressure. The pneumatic pressure output of the converter 32 is coupled to a pressure-to-pressure amplifier 33 which outputs an amplified pneumatic pressure proportional to the input pressure. The pressure output of the amplifier 33 is coupled by output conduits 34A, 35A and 36A, respectively, to a first selection valve 34, a second selection valve 35 and a pressure reducer amplifier 36. The valve 35, as shown, is in a position where the pressure in the conduit 35A is blocked off from the rest of the system. The pressure in the conduit 34A is coupled by the position of the valve 34 to couple the pressure in conduit 34A to the conduits 37A and 37B. The conduit 37A couples to the three-way valve 26 which, in the position shown, couples pressure to the throttle control T for the engine 22 for a corresponding control of the associated pump 14. Thus, it can be appreciated that operation of the potentiometer 30 in the remote location control 29 produces an electrical control function which is converted to a pressure control by the remote throttle control 28 at the drilling location for control of the engine 22 whenever the valves 34, 26 and 35 are in the positions shown in the drawings.

The pressure reducer amplifier 36 has output conduits 38A and 38B which respectively couple the reducer 36 to the valves 34 and 35. In the position of the valves 34 and 35 shown in FIG. 2, the conduit 38A is blocked off by the position of the valve 34. The valve 35, in the position shown, couples the conduit 38B to the output conduits 39A and 39B of the valve 35. The conduit 39A couples to the three-way valve 27 which, in the position shown, conveys pressure to the throttle control T for the engine 23. The pressure reducer amplifier 36 is a conventional Ratio Control Station and available from Moore Products. The reducer amplier 36 can be selectively adjusted as schematically illustrated by the dial 40 to vary the pressure on the output side relative to the input by a fixed relationship. The device 36 can serve to either amplify or reduce the pressure as may be desired and produce a corresponding relative control function. This relationship can be ratio or percentage. Thus, the pressure control to the engine 23 is a predetermined function of the pneumatic control to the engine 22 as determined by the setting of 5 the reducer 36.

The valves 34 and 35 are selectively operable. The line and X designation to these valves schematically illustrates the switching control means which are coupled to remotely located actuating means such as a switch 39 at the remote control means 29. When the switch 39 is operated, the positions of both the valves 34 and 35 are reversed. When the positions of the valves 34 and 35 are reversed, then the pressure from the amplifier 33 is supplied via the valve 35 and the valve 27 to the engine 23 and the reduced or lesser pressure from the reducer amplifier 36 is supplied via the valves 34 and 26 to the engine 22. Hence, either pump can be the master controlled pump from the control means and the other pump can be the slave controlled pump.

The manual control means 24 is coupled by a conduit 40A to another input of the valve 26 and, in the position shown, the conduit 40A is closed or blocked off by valve 26 while the conduit 37A is coupled to the output conduit of the valve 26. The manual control means 25 is coupled by a conduit 41A to a second input for the valve 27 and, in the position shown, the conduit 41A is closed or blocked off by valve 27 while the conduit 39A is coupled to the output conduit of valve 27. The valve 26 is adapted for selective operation by a control means such as a switch 26B at the control means 29 which is connected to the control device for the valve as illustrated by the line with the designation Y1. The valve 27 is adapted for selective operation by a control means such as a switch 2713 at the control means 29 which is connected to the control device for the valve by the line with the designation Y2. Actuation of the valves 26 and 27 will reverse the pressure control from the remote control pressure lines 37A and 39A to the control of the manual control pressure lines 40A and 41A.

The conduit 37B from the valve 34 is coupled to an input of a valve 42. The valve 42, in the position shown, couples the conduit 37B to one input of a pressure comparison means 43. The conduit 398 from the valve 35 is coupled to the other input of the valve 42 and is blocked off or closed by the position of the valve 42. A conduit 40B from the manual control means 24 is coupled to one input of a valve 44. The valve 44, in the position shown, couples the conduit 40B to the other input of the pressure comparison means 43. The conduit 41B from the manual control 25 is coupled to the other input of the valve 44. The valve 44, in the position shown, closes off the conduit 41B. The input pressures transmitted by valves 42 and 44 to the compari son means 43 are compared and electrical output signals representative of any pressure difference is supplied via an electrical conduit 44 to a meter or indicator 45 in the control means 29. The indicator 45 is arranged to read null signals; i.e., indications when the pressures are equal and, in the event of inequality, how much difference exists between the pressures. Since the comparator means 43 detects differences in pressure, in the described example, it can be determined how much difference in pressure exists between the operative remotely controlled pressure controlling the engine 22 and the pressure as determined by the control setting of the inactive manual. control means 24. By the use of a control device such as an electrical switch 42B (coupled by lines identified with the character Z) for the switching control means of the valves 42 and 44, the valve positions can be reversed. Whenever the positionsiof the valves 42 and 44 are reversed the relationship of the pressure of the other manual control 25 to the control pressure for the engine 23 can be determined.

Relative to the operation of the present system, for a well drilling operation, the mud properties, hole and pipe configuration and pump characteristics are considered. Because two pumps have functionally related characteristics, their operation relative to one another to optimize their operation can be decided upon so that they can be operated in a fixed ratio relative to one another. This predetermined operational ratio is set by the operation of the selecting dial mechanism 40 of the converter 36.

The valves 26, 34, 27 and 35 may be initially set in the position shown in FIG. 2 so that the potentiometer 30 in the control means 29 can provide current signals to the current-to-pressure converter 32. The converter 32 provides a pneumatic pressure proportionally related to the current input. The pressure amplifier 33 serves to provide an amplified pressure for the system. From the amplifier 33, the pressure output is supplied to the control for the engine 22 via the open valves 34 and 26. The pressure output of the amplifier 33 is reduced to a ratio value by the pressure reducer amplifier 40 and is supplied to the control for the engine 23 via the open valves 35 and 27. As the pressure from the converter 32 is increased or decreased in response to control signals from the remote controller 29, the speed of engine 22 (and pump 14) is correspondingly increased or decreased. At the same time the control pressure to the engine 23 in proportion to pressure controlling the engine 22 proportionally increases or decreases the speed of the engine 23. Hence, in the above illustration, the pump 14 is the prime pump under control, and the pump 15 is the slave pump which is controlled in fixed relation to pump 14. If the remote control switch 348 is operated, the valves 34 and 35 respectively change position so that the primary pressure control from theconverter 32 is then supplied to the engine 23. The valves 34 and 35 thus serve as selection valves for selecting the prime pump and the follower pump to be controlled.

To convert the control operation from the remote control means 29 to the manual control means 24 and 25, the control switch 26B is operated and the control valves 26 and 27 reverse positions to couple the manual control means 24 and 25 to the engines 22 and 23, respectively. At this time the driller canassume manual control for each of the pumps.

The manual control means 24, and 25 for each of the pumps are coupled toa comparison valve 44 whilethe remote control pressures for each of the engines is coupled to a comparison .valve 42. With this arrangement and the valves 42 and 44 in the position shown in FIG. 2, the pressure in the manual control means 24 is compared to the pressure output from valve 34. In this regard the pressure comparison exists irrespective of the position of control valve means 26 relative to the engine 22. The pressures supplied to the pressure comparison means 43 provide a signal output indicative of the pressure differential to the remote meter 45. Either the potentiometer 30 or the manual control means 24 7 can be adjusted to equalize the pressures between the units. The merit of having equal pressures in the manual means and remote control means is that the control of the system can be shifted between these two modes as described above without changing the effect on the controlled engine. By operation of valves 42 and the positions of the valves can be reversed so that both manual controls can be calibrated in terms of pressure with reference to the pressure control of the remote control.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is: 1. A control system for regulating the control of at least two motive control means relative to one another comprising:

first motive control means including an electrically controllable source for producing first fluid control pressure, a manually variable source for producing a second fluid control pressure, first pressure output means, first pressure selection means coupled to said first and second fluid control pressures for selectively supplying one of said first and second fluid control pressures to said first pressure output means, second motive control means including pressure modifier means responsive to an input pressure for producing a third fluid control pressure at a modified pressure relative to said input pressure, and another manually variable source for providing a fourth fluid control pressure, said modifier means being coupled to said electrically controllable source, second pressure output means, second pressure selection means coupled to said third and fourth control pressures for selectively supplying one of said third and fourth fluid control pressures to said. second output means,

means for also supplying said first fluid control pressure to said pressure modifier means as said input pressure, and

means for comparing one of said selected ones of said fluid control pressures with one of said nonselected fluid control pressures.

2. The apparatus of claim 1 and further including means for switching said comparing means from the pressures being compared to the remaining two pressures for purposes of comparison.

3. The apparatus of claim 2 and further including means for selectively switching said first and second motive control means relative to said manual controlling means.

4. A control system for regulating the control of two pump means relative to one another comprising:

first pump means subject to control by pressure,

second pump means subject to control by pressure,

first selection valve means having two inputs and one output, second selection valve means having two inputs and one output, 1

an electrically controllable source of control pressure coupled to an input of each of said first and second selection valve means,

pressure modifier means for producing an output pressure at a predetermined modified pressure relative to an input pressure, said pressure modifier means having an input and an'output, said input being coupled to said electrically controllable source and said output being coupled to the other of said inputs of each of said first and second selection valves, the outputs of said selection valves being respectively coupled to said first and second pump means, and said selection valves being operable for coupling said electrically controllable source of control pressure to one of said pump means. 5. In a drilling operation employing at least two controllable pumps,

first pump means and second pump means each responsive to control by pressure, first manually operable, control pressure means for first pump means, second manually operable, control pressure means for second pump means, first means for developing a first control pressure, second means for developing a second control pressure, said second pressure developing means being coupled to said first pressure developing means for providing a said second control pressure at a fixed relationship relative to thepressure of said first pressure developing means, first control valve means for selectively connecting one of said first manually operable pressure means and said first pressure developing means to said first pump means, second control valve means for selectively-connecting one of said second manually operable pressure means and said second pressure developing means to said second pump means, and means for reversing the condition of said first and second control valve means and thereby respectively reversing application of control pressures to said pump means from said one pressure means to said other pressure means. 6. A control system for regulating the control of two pump means relative to one another comprising,

first pump means subject to control by pressure, a first control valve coupled to said first pump control means, I a first manually variable source of control pressure coupled to said first control valve, second pump means subject to control by pressure, a second control valve coupled to said second pump control means, a second manually variable source of control pressure coupled to said second control valve, pressure comparison means for sensing the difference in pressure between a first pressure input and a second pressure input, one of said first and second manually variable sources being coupled to one of said pressure inp an electrically controllable source of control pressure coupled to the other of said pressure inputs and to said first control valve means, pressure reducer means for producing an output pressure at a predetermined ratio of reduced pressure relative to' an input pressure, said pressure reducer means having an input and an output, said input being coupled to said electrically controllable 9 source and said output being coupled to said second control valve.

7. The control system of claim 6, wherein said pressure reducer means has means for adjusting the predetermined reduction in pressure.

8. A control system for regulating the control of two pump means relative to one another comprising,

first pump means subject to control by pressure,

a first control valve coupled to said first pump control means,

a first manually variable source of control coupled to said first control valve, second pump means subject to control by pressure,

a second control valve coupled to said second pump control means,

a second manually variable source of control pressure coupled to said second control valve, pressure comparison means for sensing the difference in pressure between a first pressure input and a second pressure input, first comparison valve means coupled to said first pressure input and second comparison valve means coupled to said second pressure input,

each of said first and second manually variable sources being coupled to said second comparison valve means, said second comparison valve means being operable for coupling of one of said manually variable sources to said second input,

first selection valve means having two inputs and one output,

second selection valve means having two inputs and one output,

an electrically controllable source of hydraulic control pressure coupled to an input of each of said first and second selection valve means,

pressure ratio means for producing an output pressure at a pressure relative to an input pressure, said pressure ratio means having an input and an output, said input being coupled to said electrically controllable source and said output being coupled to the other of said inputs of each of said first and second selection valves, the outputs of said selection valves being respectively coupled to said first and second control valves, said selection valves being operable for coupling said electrically controllable source of control pressure to one of said control valves and for coupling said pressure ratio means to the other of said control valves, the outputs of said selection valves also respectively being coupled to said first comparison valve means for supplying pressure from one of said selection valve means to said pressure comparison means.

9. The control system of claim 8 wherein said pressure reducer means has means for adjusting the predetermined reduction in pressure.

10. In a drilling system for controlling the speed of one operating unit and obtaining a fixed relative control of the speed of a second operating unit with respect to the speed of said first operating unit, apparatus comprising:

at least two operating units, each of said units having their speed of operation controllable by control fluid pressures,

pressure generating means for developing a first control fluid pressure for one of said units,

means coupled to said pressure generating'm'e'ans for selectively producing a second control fluid pressure with a ratio relationship relative to said first pressure 1'10 control fluid pressure for the other of said hydraulic units, and

means for varying said first'control fluid pressure of said pressure generating means for varying the second control pressure to said other unit in a ratio relationship relative to said first fluid pressure.

11. The drilling system of claim 10, and further including means for reversing the application of said first and second control pressures to said units.

12. In a drilling system for obtaining compound control of the relative speed of at least two operating units, a system comprising:

first and second speed controllable operating units for providing a drilling function, first control means for providing a first control function for the speed of said first controllable unit,

second control means for providing a second control function for the speed of said second controllable unit, and

means coupling said second control means to said first control means and responsive to said first control means to slave the control function of said second unit to the control function of said first unit, said coupling means including a selectively adjustable ratio device for maintaining a predetermined relationship between the speed control functions of said control means.

13. A pressure control system for regulating the speed control function of two pump means relative to one another comprising:

first pump means having a speed control means subject to control by a pressure function,

second pump means having a speed control means subject to control by a pressure function,

an electrically controllable source of a control pressure function coupled to one of said speed control means of said pump means,

pressure modifier means for producing an output pressure function at a predetermined different pressure relative to an input pressure, said pressure modifier means having input means and output means, said input means being coupled to said electrically controllable source and said output means being coupled to the said speed control means of said other pump means.

14. The control system of claim 13 wherein said pressure modifier means includes means for adjusting the amplification of the output pressure function relative to the input control pressure function.

.15. A control system for regulating the control of at least two motive control means relative to one another comprising:

first motive control means including an electrically controllable source for producing first fluid control pressure, a manually variable source for producing a second fluid control pressure, first pressure output means, first pressure selection means coupled to said first and second fluid control pressures for selectively supplying one of said first and second fluid control pressures to said first pressure output means,

second motive control means including pressure modifier means responsive to an input pressure for producing a third fluid control pressure at a modified pressure relative to said input pressure, and another manually variable source for providing a fourth fluid control pressure, said modifier means being coupled to said electrically controllable 1 1 source, second pressure output means, second pressure selection means coupled to said third and fourth control pressures for selectively supplying one of said third and fourth fluid control pressures to said second output means, and means for also supplying said first fluid control pressure to said pressure modifier means as said input pressure. 16. In a drilling system for controlling the speed of one operating unit and obtaining a relative control of the speed of a second operating unit with respect to the speed of said first operating unit, apparatus comprising: a first operating unit having an independent output function and having a speed control means respon- 12 sive-to a first control pressure for regulating said output function,

a second operating unit having an independent output function and having a speed control means re-' sponsive to a second control pressure for regulating said output functions,

means for generating said first control pressure and applying said first control pressureto said first operating unit,

means responsive to said first control pressure for generating a second control pressure having a controlled dependent function relative to said first control pressure, and

means for coupling said second control pressure to said second operating unit. 

1. A control system for regulating the control of at least two motive control means relative to one another comprising: first motive control means including an electrically controllable source for producing first fluid control pressure, a manually variable source for producing a second fluid control pressure, first pressure output means, first pressure selection means coupled to said first and second fluid control pressures for selectively supplying one of said first and second fluid control pressures to said first pressure output means, second motive control means including pressure modifier means responsive to an input pRessure for producing a third fluid control pressure at a modified pressure relative to said input pressure, and another manually variable source for providing a fourth fluid control pressure, said modifier means being coupled to said electrically controllable source, second pressure output means, second pressure selection means coupled to said third and fourth control pressures for selectively supplying one of said third and fourth fluid control pressures to said second output means, means for also supplying said first fluid control pressure to said pressure modifier means as said input pressure, and means for comparing one of said selected ones of said fluid control pressures with one of said non-selected fluid control pressures.
 2. The apparatus of claim 1 and further including means for switching said comparing means from the pressures being compared to the remaining two pressures for purposes of comparison.
 3. The apparatus of claim 2 and further including means for selectively switching said first and second motive control means relative to said manual controlling means.
 4. A control system for regulating the control of two pump means relative to one another comprising: first pump means subject to control by pressure, second pump means subject to control by pressure, first selection valve means having two inputs and one output, second selection valve means having two inputs and one output, an electrically controllable source of control pressure coupled to an input of each of said first and second selection valve means, pressure modifier means for producing an output pressure at a predetermined modified pressure relative to an input pressure, said pressure modifier means having an input and an output, said input being coupled to said electrically controllable source and said output being coupled to the other of said inputs of each of said first and second selection valves, the outputs of said selection valves being respectively coupled to said first and second pump means, and said selection valves being operable for coupling said electrically controllable source of control pressure to one of said pump means.
 5. In a drilling operation employing at least two controllable pumps, first pump means and second pump means each responsive to control by pressure, first manually operable, control pressure means for first pump means, second manually operable, control pressure means for second pump means, first means for developing a first control pressure, second means for developing a second control pressure, said second pressure developing means being coupled to said first pressure developing means for providing a said second control pressure at a fixed relationship relative to the pressure of said first pressure developing means, first control valve means for selectively connecting one of said first manually operable pressure means and said first pressure developing means to said first pump means, second control valve means for selectively connecting one of said second manually operable pressure means and said second pressure developing means to said second pump means, and means for reversing the condition of said first and second control valve means and thereby respectively reversing application of control pressures to said pump means from said one pressure means to said other pressure means.
 6. A control system for regulating the control of two pump means relative to one another comprising, first pump means subject to control by pressure, a first control valve coupled to said first pump control means, a first manually variable source of control pressure coupled to said first control valve, second pump means subject to control by pressure, a second control valve coupled to said second pump control means, a second manually variable source of control pressure coupled to said second control valve, pressure comparison means for sensing thE difference in pressure between a first pressure input and a second pressure input, one of said first and second manually variable sources being coupled to one of said pressure inputs, an electrically controllable source of control pressure coupled to the other of said pressure inputs and to said first control valve means, pressure reducer means for producing an output pressure at a predetermined ratio of reduced pressure relative to an input pressure, said pressure reducer means having an input and an output, said input being coupled to said electrically controllable source and said output being coupled to said second control valve.
 7. The control system of claim 6, wherein said pressure reducer means has means for adjusting the predetermined reduction in pressure.
 8. A control system for regulating the control of two pump means relative to one another comprising, first pump means subject to control by pressure, a first control valve coupled to said first pump control means, a first manually variable source of control pressure coupled to said first control valve, second pump means subject to control by pressure, a second control valve coupled to said second pump control means, a second manually variable source of control pressure coupled to said second control valve, pressure comparison means for sensing the difference in pressure between a first pressure input and a second pressure input, first comparison valve means coupled to said first pressure input and second comparison valve means coupled to said second pressure input, each of said first and second manually variable sources being coupled to said second comparison valve means, said second comparison valve means being operable for coupling of one of said manually variable sources to said second input, first selection valve means having two inputs and one output, second selection valve means having two inputs and one output, an electrically controllable source of hydraulic control pressure coupled to an input of each of said first and second selection valve means, pressure ratio means for producing an output pressure at a pressure relative to an input pressure, said pressure ratio means having an input and an output, said input being coupled to said electrically controllable source and said output being coupled to the other of said inputs of each of said first and second selection valves, the outputs of said selection valves being respectively coupled to said first and second control valves, said selection valves being operable for coupling said electrically controllable source of control pressure to one of said control valves and for coupling said pressure ratio means to the other of said control valves, the outputs of said selection valves also respectively being coupled to said first comparison valve means for supplying pressure from one of said selection valve means to said pressure comparison means.
 9. The control system of claim 8 wherein said pressure reducer means has means for adjusting the predetermined reduction in pressure.
 10. In a drilling system for controlling the speed of one operating unit and obtaining a fixed relative control of the speed of a second operating unit with respect to the speed of said first operating unit, apparatus comprising: at least two operating units, each of said units having their speed of operation controllable by control fluid pressures, pressure generating means for developing a first control fluid pressure for one of said units, means coupled to said pressure generating means for selectively producing a second control fluid pressure with a ratio relationship relative to said first control fluid pressure for the other of said hydraulic units, and means for varying said first control fluid pressure of said pressure generating means for varying the second control pressure to said other unit in a ratio relationship relative to said first fluid pressure.
 11. The drilling system of claim 10, and further including means for reversing the application of said first and second control pressures to said units.
 12. In a drilling system for obtaining compound control of the relative speed of at least two operating units, a system comprising: first and second speed controllable operating units for providing a drilling function, first control means for providing a first control function for the speed of said first controllable unit, second control means for providing a second control function for the speed of said second controllable unit, and means coupling said second control means to said first control means and responsive to said first control means to slave the control function of said second unit to the control function of said first unit, said coupling means including a selectively adjustable ratio device for maintaining a predetermined relationship between the speed control functions of said control means.
 13. A pressure control system for regulating the speed control function of two pump means relative to one another comprising: first pump means having a speed control means subject to control by a pressure function, second pump means having a speed control means subject to control by a pressure function, an electrically controllable source of a control pressure function coupled to one of said speed control means of said pump means, pressure modifier means for producing an output pressure function at a predetermined different pressure relative to an input pressure, said pressure modifier means having input means and output means, said input means being coupled to said electrically controllable source and said output means being coupled to the said speed control means of said other pump means.
 14. The control system of claim 13 wherein said pressure modifier means includes means for adjusting the amplification of the output pressure function relative to the input control pressure function.
 15. A control system for regulating the control of at least two motive control means relative to one another comprising: first motive control means including an electrically controllable source for producing first fluid control pressure, a manually variable source for producing a second fluid control pressure, first pressure output means, first pressure selection means coupled to said first and second fluid control pressures for selectively supplying one of said first and second fluid control pressures to said first pressure output means, second motive control means including pressure modifier means responsive to an input pressure for producing a third fluid control pressure at a modified pressure relative to said input pressure, and another manually variable source for providing a fourth fluid control pressure, said modifier means being coupled to said electrically controllable source, second pressure output means, second pressure selection means coupled to said third and fourth control pressures for selectively supplying one of said third and fourth fluid control pressures to said second output means, and means for also supplying said first fluid control pressure to said pressure modifier means as said input pressure.
 16. In a drilling system for controlling the speed of one operating unit and obtaining a relative control of the speed of a second operating unit with respect to the speed of said first operating unit, apparatus comprising: a first operating unit having an independent output function and having a speed control means responsive to a first control pressure for regulating said output function, a second operating unit having an independent output function and having a speed control means responsive to a second control pressure for regulating said output functions, means for generating said first control pressure and applying said first control pressure to said first operating unit, means responsive to said first control pressure for generAting a second control pressure having a controlled dependent function relative to said first control pressure, and means for coupling said second control pressure to said second operating unit. 